Several optical systems are known to allow a three-dimensional image created based on an object to be seen, some of which systems are straightforward but nevertheless have the drawback that the images reproduced have their signs specularly inverted from left to right and are therefore almost illegible, all of which requires that the objects be labelled with specularly inverted characters and words and phrases be written from right to left in order to allow them to be properly read on observing the three-dimensional image.
There are also more complex optical systems which comprise a greater number of elements or more sophisticated elements, such as semi-transparent and/or polarised sheets, which may, depending on their position, generate unwanted simultaneous images of the object, of the observers themselves or of elements existing in their surroundings.
In conclusion, creating a three-dimensional image in space is achieved either with inverted signs or based on more complex systems which may generate other images along with the image of the object.